How were officers trained?

[Epictetus]

Since there was no formal "military academy", and Rome ran on personal connections, any tribune position would depend on influence and favors. But it really looks like those equestrians that made it to a legion would at least be competent, whereas it's quite possible that many senatorial tribunes were still just traditional good-old-boy appointments.

Military tribunes and their significance

You know, I've been wondering about this recently. Exactly how were they trained? Would a child growing up in a powerful family receive military training in the expectation of his future career? Once he got his first appointment, would he have a mentor? How would he be trained in tactics, strategy, logistics... even the art of commanding men?

I would assume that the training of officers was at least as important as the training of men, but I really don't know anything about how it worked. I recall reading quite a bit about the training of soldiers, but nothing about the training of their commanders.